Zirconium Phosphate Particles Having Improved Adsorption Capacity And Method Of Synthesizing The Same

ABSTRACT

Zirconium phosphate particles are synthesized by providing a solution of zirconium oxychloride in an aqueous solvent, adding at least one low molecular weight, oxygen containing, monofunctional, organic additive to the solution, and combining this solution with heated phosphoric acid or a phosphoric acid salt to obtain zirconium phosphate particles by sol gel precipitation.

This application claims the benefit under 35 U.S.C. §119(e) of priorU.S. Provisional Patent Application No. 61/102,466, filed Oct. 3, 2008,which is incorporated in its entirety by reference herein.

FIELD OF INVENTION

The present invention relates to zirconium phosphate particles, and tomethods of making zirconium phosphate particles, such as by sol gelsynthesis, that have improved porosity, BET surface area, and/orammonium ion adsorption properties.

BACKGROUND OF THE INVENTION

Zirconium phosphate (ZrP) particles are used as ion exchange materialsand are particularly useful as a sorbent material for regenerativedialysis. Zirconium phosphate (ZrP) particles can be synthesized by asol gel process using zirconium oxychloride (ZOC), also called zirconylchloride, as a starting material. ZOC is a preferred starting materialbecause it is abundant and commercially available at a low price.

Sol gel precipitation, as the term is used herein, refers generally to aprocess for forming a ceramic or catalyst in which colloidal particles(called sol) are formed by reacting hydrated metal ions (group III andIV) with a precipitating agent, followed by the polymerization of thecolloidal particles to form gel particles. See, for example, Bogdanov SG et al., “Structure of zirconium phosphate gels produced by the sol-gelmethod,” J. PHYS.: CONDENS. MATTER, Vol. 9, 4031-4039 (1997),incorporated herein by reference. Sol gel precipitation is aparticularly advantageous method of obtaining zirconium phosphate fromzirconium oxychloride since it is a direct, single-step conversionprocess that can be carried out at room temperature. Hence, it offersgreat advantages in efficiency and manufacturing costs in comparisonwith other processes. Moreover, zirconium phosphate particles obtainedby sol gel precipitation generally have a high porosity and a high BETsurface area, which enhances their adsorption capacity for ammonia.Further, the use of the sol gel precipitation method allows for controlover particle size and morphology of the product, as well as controlover impurity levels. These characteristics for zirconium phosphateparticles are important with respect to ammonia adsorption and cartridgedesign for dialysis applications.

Despite all of these advantages, the sol gel precipitation is not easyto accomplish on a manufacturing scale. The difficulties are mainlycaused by the nature of the raw material (e.g., ZOC), the rapid rate ofthe reaction, which is difficult to control, and the lack of appropriateprocess control methods (flow rate, agitation rate, concentration,etc.). These difficulties can be described as follows.

Sol gel zirconium phosphate, when precipitated directly from zirconiumoxychloride solution using phosphoric acid as a precipitating agent, isin the form of soft gel particles having a wide range of particle sizes.One reason why this happens is that zirconium ions in a solution ofzirconium oxychloride are highly hydrated monomers, that is, they aresurrounded by a large number of coordinated water molecules. During theformation of zirconium phosphate, the soft gel particles tend toagglomerate when the product slurry gets thicker during the reactionprocess, or when the particles are packed during the filtration anddrying process. As a result of this agglomeration, large aggregates arepresent in the end product after drying so that milling or grinding isrequired to obtain a free-flowing powder, with the further disadvantagethat milling produces a lot of excessively fine particles. Agglomerationalso increases the particle size to an extent that is undesirable forcolumn or separation applications.

A wide range of particle sizes in the finished product is a commonresult of the conventional sol gel precipitation process for theadditional reason that the particle size depends on the concentration ofthe reactants, which gradually decreases as precipitation continues,causing the formation of smaller particles. Thus, it is difficult tocontrol particle size using a single reactant addition technique. Largeparticles and excessively fine particles are both undesirable fordialysis application because large particles can cause ammonia leakageand smaller adsorption capacity, while fine particles can increase flowresistance and pressure drop in a sorbent cartridge.

Further, the agglomeration of sol gel zirconium phosphate during theprecipitation process interferes with agitation and mixing of thereactants as the slurry concentration increases, resulting in theformation of an excessive number of fine particles.

The particle size of sol gel zirconium phosphate can be increased byincreasing the amount and concentration of phosphoric acid (for example,by providing a ratio of ZrO₂:PO₄ of 1:3) but the increase in phosphoricacid also enhances the gelation effect as excess lattice H⁺ in ZrPcombines with H₂O molecules.

Recent advances in sol gel precipitation provide a method ofsynthesizing zirconium phosphate particles that avoids the creation ofsoft gel particles and/or that avoids agglomeration of zirconiumphosphate gel particles. U.S. Patent Application Publication No.2006/0140840, which is incorporated in its entirety by reference herein,describes a method for synthesizing zirconium phosphate particles thatutilizes organic chemical additives to suppress gelation andagglomeration in order to control particle size of the product. Theadditive is added to a zirconium oxychloride solution and can form acomplex with zirconium ions in the solution and thereby reduce hydrationof the zirconium ions. The solution can then be combined with phosphoricacid or a phosphoric acid salt to obtain zirconium phosphate particlesby sol gel precipitation. The method can synthesize zirconium phosphateparticles having a controlled particle size or particle sizedistribution. Zirconium phosphate particles synthesized by this methodcan have, for example, a particle size distribution of less than 20% inthe range of >60-120 microns, more than 80% in the range of 30-60microns, and less than 10% in the range of less than 30 microns. Theparticles can also have an ammonia capacity in dialysate solution ofabout 15-20 mg NH₄ ⁺—N/g ZrP, when exposed to an NH₄ ⁺—N/g concentrationof 100 mg/dL.

Despite the controlled particle size and tight particle sizedistribution, the zirconium phosphate particles may reflect a largerparticle size than desired, and lower than expected ammonium ionadsorption capacity. Residual organic additives may be tightly bound tothe ZrP lattice and as a result, the porosity and BET surface area ofthe particles may be less than expected.

Accordingly, there is a need for an improved method of synthesizingzirconium phosphate particles that overcomes one or more of theabove-mentioned disadvantages.

There is a need for a sol gel preparation method that removes anyresidual organic additives from the sol gel ZrP product, thus improvingporosity, BET surface area, and NH₄ ⁺ adsorption capacity.

There is a particular need for ZrP particles smaller than about 5microns that can have enhanced NH₄ ⁺ adsorption capacity sol gel ZrPparticles for sorbent applications including portable sorbent dialysissystems.

SUMMARY OF THE INVENTION

A feature of the present invention is to provide zirconium phosphateparticles that avoid one or more of the above-mentioned disadvantages.

A feature of the present invention is to provide zirconium phosphateparticles having a desirable hardness, particle size, particle sizerange, shape, packing density, porosity, BET surface area foradsorption, and/or adsorption capacity.

Another feature of the present invention is to provide zirconiumphosphate particles having improved porosity, BET surface area, and/orammonium ion adsorption capacity.

Another feature of the present invention is to provide zirconiumphosphate particles having an average particle size of less than 5microns.

A further feature of the present invention is to provide zirconiumphosphate particles prepared by sol gel precipitation having no (oressentially no) residual organic molecules bound to the particle.

A feature of the present invention is to provide a method ofsynthesizing zirconium phosphate particles by a sol gel technique thatavoids one or more of the above-mentioned disadvantages.

Another feature of the present invention is to provide a method ofsynthesizing zirconium phosphate particles by a sol gel technique thatavoids the creation of soft gel particles and/or that avoidsagglomeration of zirconium phosphate gel particles, and that does notresult in residual organic molecules bound to the particles to reduceporosity, BET surface area, and/or ammonia adsorption capacity.

Additional advantages of the present invention will be set forth in partin the description that follows, and in part will be apparent from thedescription, or may be learned by practice of the present invention. Thegoals and advantages of the present invention will be realized andattained by means of the elements particularly pointed out in theappended claims.

To achieve the above noted goals and in accordance with the purposes ofthe present invention, as embodied and broadly described herein, thepresent invention provides a composition comprising a water-solublezirconium-containing polymer complex in an aqueous solution, wherein thepolymer complex is formed by combining, in an aqueous solvent, zirconiumoxychloride with at least one low molecular weight, oxygen containing,monofunctional, organic additive. The additive can form a complex withzirconium ions in the solution.

The present invention also provides zirconium phosphate particlessynthesized by a sol gel precipitation that do not include tightly boundresidual organic compounds.

The present invention further provides zirconium phosphate particleshaving one or more of the following characteristics: an average particlesize of less than 5 microns, an ammonia capacity in dialysate solutionof at least 15 mg NH₄—N/g ZrP when exposed to 100 mg/dL of NH₄—N, and/ora BET surface area of at least about 10 m²/g ZrP.

The present invention further provides a portable dialysis systemcomprising a container that contains such zirconium phosphate particles.

The present invention further provides zirconium phosphate particlescomprising one or more of the following characteristics: an averageparticle size of from about 40-50 microns, an ammonia capacity indialysate solution of at least 15 mg NH₄—N/g ZrP when exposed to 100mg/dL of NH₄—N, and/or a BET surface area of at least about 10 m²/g ZrP.

The present invention further provides a dialysis cartridge comprising acartridge that contains such zirconium phosphate particles.

The present invention further provides zirconium phosphate particlescomprising one or more of the following characteristics: an averageparticle size of from about 45-90 microns, an ammonia capacity indialysate solution of at least 15 mg NH₄—N/g ZrP when exposed to 20mg/dL of NH₄—N, and/or a BET surface area of at least about 2 m²/g ZrP.

The present invention further provides a dialysis cartridge comprising acartridge that contains such zirconium phosphate particles.

The present invention further provides zirconium phosphate particlescomprising one or more of the following characteristics: a pore volumeof at least 0.0071 mL/g, a monolayer volume of at least 0.5 mL/g (STP),and/or a 20-80 nm pore size content of at least 30%. These porosity andpore size properties can apply to any particle size, including anyparticle size range indicated herein. Also, for example, these particlescan have a BET surface area of at least about 2 m²/g ZrP, or at leastabout 5 m²/g ZrP, or at least about 10 m²/g ZrP.

The present invention further provides a dialysis cartridge comprising acartridge that contains such zirconium phosphate particles.

The present invention also provides a method of making zirconiumphosphate particles by combining zirconium oxychloride and at least onelow molecular weight, oxygen containing, monofunctional, organicadditive, in an aqueous solvent to form a solution. The low molecularweight, oxygen containing, monofunctional, organic additive(s) can forma complex with zirconium ions in the solution and thereby reducehydration of the zirconium ions. The organic additive can preventagglomeration of the zirconium phosphate particles in sol gelprecipitation, and thereby increase the porosity and/or BET surface areaof the particles. Zirconium phosphate particles having increasedporosity and/or BET surface area can have improved ammonia adsorptioncapacity.

The low molecular weight, oxygen containing, monofunctional, organicadditive(s) either does not bind or tightly bind to the zirconiumphosphate particles. Accordingly, the method further includes combiningthe solution with phosphoric acid or a phosphoric acid salt, and thenremoving the low molecular weight, oxygen containing, monofunctional,organic additive to obtain zirconium phosphate particles free of (oressentially free of) residual additive by sol gel precipitation. The lowmolecular weight, oxygen containing, monofunctional, organic additivecan be removed, for example, by evaporating the additive to obtainzirconium phosphate particles that are free of (or essentially free of)residual organic additive. The phosphoric acid or phosphoric acid saltcan be at boiling temperature, for example, a temperature of from about90° C.-100° C., or about 96° C. The low molecular weight, oxygencontaining, monofunctional, organic additive can also be removed, suchas by washing the zirconium phosphate particles, for example, withwater, to remove residual organic additive. Other removal techniques canbe used.

The low molecular weight, oxygen containing, monofunctional, organicadditive can be removed by any technique, such as by heat and/orwashing, and the like. For purposes of the present invention, the“removal” of the additives can include total removal of the additiveand/or substantial removal of the additive, such as preferably below 1wt % (e.g., 0 wt % to 0.9 wt %, 0.0001 wt % to 0.7 wt %, 0.001 wt % to0.5 wt %, 0.01 wt % to 0.25 wt %) of the additive remaining, based onthe total weight of the additive present prior to the removal.Subjecting the zirconium phosphate particles to heat, such as theboiling temperature of the phosphoric acid, can evaporate a lowmolecular weight, oxygen containing, monofunctional, organic additiveand remove the residual additive from the zirconium phosphate particles,thus optionally increasing porosity and/or BET surface area. The heatstep can have a hardening effect on the particles and/or improve thecrystal structure of the particles. Hardened zirconium phosphateparticles can be dried without suffering from particle collapse and/oragglomeration. The method can optionally further include subjecting anaqueous slurry containing the zirconium phosphate particles toadditional heat treatment, for example, for about 1-2 hrs, for instance,at a temperature of, for example, from about 90° C.-100° C.

The present invention further provides a method of synthesizingzirconium phosphate particles having a controlled particle size orparticle size distribution. The method includes combining a solution ofzirconium oxychloride and low molecular weight, oxygen containing,monofunctional, organic additive with a solution of phosphoric acid or aphosphoric acid salt and evaporating the low molecular weight, oxygencontaining, monofunctional, organic additive to obtain zirconiumphosphate particles by sol gel precipitation. For instance, the methodcan include providing a reaction vessel having an agitator and adding asolution of zirconium oxychloride and a solution of phosphoric acid or aphosphoric acid salt, such as simultaneously (or other orders ofaddition) to the reaction vessel so that zirconium ions react with thephosphoric acid or a phosphoric acid salt to obtain zirconium phosphateparticles by sol gel precipitation. The particle size and/or particlesize distribution of the zirconium phosphate particles obtained can becontrolled by controlling at least one or more of the followingparameters: the rate at which the solution of zirconium oxychloride isadded to the reaction vessel, the rate at which the solution ofphosphoric acid or phosphoric acid salt is added to the reaction vessel,the pH of the solution of phosphoric acid or phosphoric acid salt, theconcentration of each component, i.e., zirconium oxychloride, lowmolecular weight, oxygen containing, monofunctional, organic additive,and/or phosphoric acid or a phosphoric acid salt in the reaction vessel,the addition of hydrochloric acid (HCl) to the reaction, the speed ofthe agitator, or combinations thereof.

The present invention further provides a method of synthesizingzirconium phosphate particles by combining zirconium oxychloride and atleast one low molecular weight, oxygen containing, monofunctional,organic additive in an aqueous solvent, to form a solution wherein thelow molecular weight, oxygen containing, monofunctional, organicadditive(s) can form a complex with zirconium ions in the solution,which can reduce hydration of the zirconium ions, combining the solutionwith phosphoric acid or a phosphoric acid salt, and evaporating the atleast one low molecular weight, oxygen containing, monofunctional,organic additive to obtain zirconium phosphate particles by sol gelprecipitation. The method can further include subjecting an aqueousslurry containing the zirconium phosphate particles to a heat treatment.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary only and are notrestrictive of the present invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this application, illustrate some of the embodiments of thepresent invention and together with the description, serve to explainthe principles of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section of a sorbent cartridge used for a productquality-cartridge performance test based on NH₄ ⁺—N adsorption capacityof the cartridge.

FIG. 2 is a graph showing the dependence of particle swelling, asswelling volume (cm³/kg), on an additive that is combined with zirconiumoxychloride before precipitation with phosphoric acid for sol-gelproduction.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates in part to zirconium phosphate particleshaving improved porosity, BET surface area, and/or ammonium ionadsorption capacity. The zirconium phosphate (ZrP) particles can have,for example, one or more of the following characteristics: an averageparticle size of less than 5 microns, for example, from about 2 to 4.9microns or from about 1 to about 3 microns or from about 0.5 to about 4microns, an ammonia capacity in dialysate solution of at least 15 mgNH₄—N/g ZrP when exposed to 100 mg/dL of NH₄—N, and/or a BET surfacearea of at least about 10 m²/g ZrP (e.g., 10 m²/g ZrP to 100 m²/g ZrP ormore, 15 m²/g ZrP to 100 m²/g ZrP, or 20 m²/g ZrP to 100 m²/g ZrP).Preferably, the ZrP particles can have an ammonia capacity in dialysatesolution of at least 20 mg NH₄—N/g ZrP, and more preferably, at least 25mg NH₄—N/g ZrP, or at least 30 mg NH₄—N/g ZrP (such as 21 to 35 mgNH₄—N/g ZrP), when exposed to 100 mg/dL of NH₄—N. The ZrP particles canhave an ammonia capacity in dialysate solution of, for example, fromabout 23-26 mg NH₄—N/g ZrP, when exposed to 100 mg/dL of NH₄—N, and/oran ammonia capacity of, for example, from about 7-9 mg NH₄—N/g ZrP, whenexposed to 10 mg/dL of NH₄—N.

For purposes of this invention, a “dialysate solution” means a solutionthat can be used in hemodialysis or peritoneal dialysis, and, forexample, having a sodium chloride concentration of about 105 mEq, and asodium bicarbonate concentration of about 35 mEq. The sodiumconcentration of the dialysate solution can affect the ZrP ammoniacapacity, and the ZrP particles can have an ammonia capacity in purewater that is greater than the ammonia capacity in dialysate solution.The ZrP particles can have an ammonia capacity in pure water of, forexample, greater than 35 mg NH₄—N/g ZrP, when exposed to 100 mg/dL ofNH₄—N, greater than 30 mg NH₄—N/g ZrP when exposed to 20 mg/dL of NH₄—N,for example, from about 30-38 mg NH₄—N/g ZrP, and greater than 20 mgNH₄—N/g ZrP when exposed to 10 mg/dL of NH₄—N, for example, from about20-28 mg NH₄—N/g ZrP.

The zirconium phosphate particles of the present invention can besynthesized, for example, by combining zirconium oxychloride (ZOC) withat least one low molecular weight, oxygen containing, monofunctional,organic additive in an aqueous solvent to form a solution (organicadditive—ZOC solution), combining the solution with phosphoric acid, andevaporating, and/or washing away, the low molecular weight, oxygencontaining, monofunctional, organic additive to obtain zirconiumphosphate particles by sol gel precipitation that are free (oressentially free) of residual organic additive. The low molecularweight, oxygen containing, monofunctional, organic additive can beevaporated, for example, by vacuum, and/or heat. The organicadditive-ZOC solution can be combined with heated phosphoric acid at atemperature high enough to evaporate the organic additive, for example,up to the boiling temperature of phosphoric acid, or phosphoric acid ata temperature of, for example, from about 90° C.-100° C.

The present invention also relates in part to zirconium phosphateparticles having one or more of the following characteristics: anaverage particle size of from about 25-65 microns, for example, about40-50 microns, an ammonia capacity in dialysate solution of at least 15mg NH₄—N/g ZrP when exposed to 100 mg/dL of NH₄—N, and a BET surfacearea of at least about 10 m²/g ZrP (e.g., 10 m²/g ZrP to 100 m²/g ZrP ormore, 15 m²/g ZrP to 100 m²/g ZrP, or 20 m²/g ZrP to 100 m²/g ZrP).Preferably, the ZrP particles can have an ammonia capacity in dialysatesolution of at least 20 mg NH₄—N/g ZrP, more preferably at least 25 mgNH₄—N/g ZrP, or at least 30 mg NH₄—N/g ZrP (e.g., 25 to 35 mg NH₄—N/gZrP), when exposed to 100 mg/dL of NH₄—N. The ZrP particles can have anammonia capacity in dialysate solution of, for example, from about 21-23mg NH₄—N/g ZrP, when exposed to 100 mg/dL of NH₄—N, and/or an ammoniacapacity of, for example, from about 6-8 mg NH₄—N/g ZrP, when exposed to10 mg/dL of NH₄—N.

The present invention also relates in part to zirconium phosphateparticles having one or more of the following characteristics: anaverage particle size of from about 45-840 microns, for example, about45-90 microns, an ammonia capacity in dialysate solution of at least 15mg NH₄—N/g ZrP when exposed to 20 mg/dL of NH₄—N, and a BET surface areaof at least about 2 m²/g ZrP (e.g., 2 m²/g ZrP to 100 m²/g ZrP or more,or 5 m²/g ZrP to 100 m²/g ZrP, or 10 m²/g ZrP to 100 m²/g ZrP, or 15m²/g ZrP to 75 m²/g ZrP, or 20 m²/g ZrP to 50 m²/g ZrP). Preferably, theZrP particles can have an ammonia capacity in dialysate solution of atleast 15 mg NH₄—N/g ZrP, and more preferably, at least 20 mg NH₄—N/gZrP, or at least 25 mg NH₄—N/g ZrP (such as 20 to 35 mg NH₄—N/g ZrP, or21 to 30 mg NH₄—N/g ZrP, or 22 to 25 mg NH₄—N/g ZrP), when exposed to 20mg/dL of NH₄—N. The ZrP particles also can have an ammonia capacity indialysate solution of at least 20 mg NH₄—N/g ZrP, or at least 25 mgNH₄—N/g ZrP, or at least 30 mg NH₄—N/g ZrP (such as 20 to 35 mg NH₄—N/gZrP, or 22 to 30 mg NH₄—N/g ZrP, or 24 to 28 mg NH₄—N/g ZrP), whenexposed to 30 mg/dL of NH₄—N. The ZrP particles also can have an ammoniacapacity in pure water of at least 25 mg NH₄—N/g ZrP, or at least 30 mgNH₄—N/g ZrP, or at least 40 mg NH₄—N/g ZrP (such as 25 to 55 mg NH₄—N/gZrP, or 30 to 50 mg NH₄—N/g ZrP, or 35 to 45 mg NH₄—N/g ZrP), whenexposed to 20 mg/dL of NH₄—N. The ZrP particles also can have an ammoniacapacity in pure water of at least 30 mg NH₄—N/g ZrP, or at least 35 mgNH₄—N/g ZrP, or at least 45 mg NH₄—N/g ZrP (such as 30 to 65 mg NH₄—N/gZrP, or 35 to 60 mg NH₄—N/g ZrP, or 40 to 55 mg NH₄—N/g ZrP), whenexposed to 30 mg/dL of NH₄—N.

The present invention also relates in part to zirconium phosphateparticles having one or more of the following characteristics: a porevolume of at least 0.0071 mL/g (e.g., 0.0071 to 0.15 mL/g, or 0.0075 to0.125 mL/g, or 0.01 to 0.1 mL/g, or 0.02 to 0.09 mL/g), a (Langmuir)monolayer volume of at least 0.5 mL/g (STP) (e.g., 0.5 to 10 mL/g (STP),or 1 to 8 mL/g (STP), or 2.5 to 6.5 mL/g (STP), or 3 to 5 mL/g (STP)),and/or a 20-80 nm pore size content of at least 30% (e.g., 30% to 60%,or 32% to 55%, or 38% to 52%, or 42% to 50%). As indicated, theseporosity and pore size properties can apply to any particle size,including any particle size range indicated herein. The pore sizecontent refers to the percentage of all particle surface pores that havea pore size in the 20-80 nm range.

The particles with these porosities and pore sizes also can have, forexample, one or more of the BET surface area, the ammonia capacity indialysate solution, and/or the ammonia capacity in pure water, for anyZrP particles such as indicated herein, including, for example, but notlimited to, the ZrP particles having an average particle size of fromabout 45-90 microns. The particle size range values indicated herein asaverage particle sizes can in addition or alternatively refer to aparticle size fraction. For example, a particle size given as 45-90microns herein, also can refer to the fraction of a particulate sampleof which the particles have absolute particle sizes within that range.

The zirconium phosphate particles of the present invention can besynthesized, for example, by combining zirconium oxychloride (ZOC) withat least one low molecular weight, oxygen containing, monofunctional,organic additive in an aqueous solvent to form a solution, adding acid,like concentrated hydrochloric acid (HCl) to the solution, thencombining the solution with an acid, like phosphoric acid, andevaporating or otherwise removing essentially all of the low molecularweight, oxygen containing, monofunctional, organic additive to obtainzirconium phosphate particles by sol gel precipitation. The addition ofan acid, like HCl, can affect the average zirconium phosphate particlesize. The size of the zirconium phosphate particles can be varied toobtain particles of a desired size, for example, an average particlesize of from about 10-100 microns, about 10-25 microns, about 20-40microns, about 25-65 microns, or about 40-50 microns. Without beingbound to any theory, an acid, like HCl, may affect particle size byremoving functional OH⁻ groups from the zirconium phosphatepolymerization reaction, thus allowing the polymerization reaction tocontinue and growing the particle size.

The present invention further relates to a composition formed as anintermediate in the method of the present invention by combining azirconium oxychloride solution with a low molecular weight, oxygencontaining, monofunctional, organic additive to form a water-solublepolymer complex, as described above. The amount of low molecular weight,oxygen containing, monofunctional, organic additive can depend on theparticular additive and can be readily determined by performancestudies. The amount of low molecular weight, oxygen containing,monofunctional, organic additive can be a minimum amount that iseffective to improve the particle size of the product. Examples ofsuitable amounts are provided below.

A dialysis cartridge comprising a cartridge that contains the zirconiumphosphate particles described herein is also a part of the presentinvention. The dialysis cartridge can be a cartridge that contains thezirconium phosphate particles, wherein the zirconium phosphate particlescan be present as at least one layer and the dialysis cartridge furthercan comprise at least one other layer(s) of sorbent material. A portabledialysis system comprising a container that contains the zirconiumphosphate particles described herein is also a part of the presentinvention. The container can contain, for example, zirconium phosphateparticles as described above, for instance, having an average particlesize of less than 5 microns, for example, about 2-5 microns, an ammoniacapacity in dialysate solution of at least 25 mg NH₄—N/g ZrP whenexposed to 100 mg/dL of NH₄—N, and a BET surface area of at least about10 m²/g ZrP.

The ZrP of the present invention can be used in any application whereZrP is used and can be used as the ZrP layer or as an additional ZrPlayer in sorbent cartridges described in U.S. Patent ApplicationPublication No. 2002-0112609 and U.S. Pat. No. 6,878,283 B2, and inSorb's REDY cartridge (e.g., see “Sorbent Dialysis Primer,” COBE RenalCare, Inc. Sep. 4, 1993 edition, and “Rx Guide to Custom Dialysis,” COBERenal Care, Inc. Revision E, September, 1993), all incorporated in theirentirety by reference herein. All embodiments using ZrP in thesepublished applications are embodiments of the present applicationwherein the ZrP of the present invention is used. For example purposesonly, various filter media sections within a tubular housing orcartridge can be used with the ZrP particles of the present invention.The housing or cartridge can include a sorbent material like a granularactivated carbon section, an immobilized enzyme section, a powderedalumina (Al₂O₃) section, a zirconium phosphate, and/or a section thatincludes a mixture of hydrous zirconium oxide of the acetate form andsodium zirconium carbonate, or sodium zirconium carbonate alone. Thedialysis cartridge can be a cartridge that contains as one or morelayers or zones the zirconium phosphate particles, wherein the dialysiscartridge has a plurality of filter media sections (or layers) includingan arrangement, starting from a first end and ending at a second end, anactivated carbon section, an immobilized enzyme section, a powderedalumina section, a zirconium phosphate section, and a sodium zirconiumcarbonate or a mixture of hydrous zirconium oxide of the acetate formand sodium zirconium carbonate section. For hemodialysis, a filtermedium adapted to remove chlorine from tap water is preferred unlesshighly purified water is used as a base for the dialysate. The mediumcan be activated carbon. Activated carbon can be used as a filter mediumto bind heavy metals, oxidants, and chloramines. An immobilized enzymesuch as urease can be used in a filter medium to convert urea toammonium carbonate by enzymatic conversion. Urease can be immobilized byadsorption, covalent bonding, intermolecular cross-linking, entrapmentwithin cross-linked polymers, microencapsulation, and containment withina semipermeable membrane device. Alumina (Al₂O₃), activated carbon,anion exchange resins, and diatomaceous earth can be used as adsorbents.Urease can be used to covalently bond water-insoluble polymers to formenzyme-polymer conjugates via activation procedures or reactivepolymers. Multifunctional reagents, for example, glutaraldehyde andhexamethylene diamine can be used to affect intermolecular cross-linkingof urease. Urease can be entrapped within a cross-linked polymer, suchas, for example, polyacrylamide gel. Urease can be microencapsulatedusing, for example, nylon, cellulose nitrate, ethyl cellulose, orpolyamide. Urease can be contained within some permeable membranedevice, such as, for example, AMICOM ultra-filtration cells, availablefrom Fisher Scientific, Pittsburgh, Pa., or DOW hollow fiber beakerdevice, from The Dow Chemical Co., Midland, Mich. The use of activatedcarbon to remove chlorine, if used, can precede the immobilized enzymemedium because chlorine can deactivate the enzyme. Cation exchangematerials can be used to bind ammonium, calcium, magnesium, potassium,and other cations as well as toxic trace metals in tap water. Anotherfunction of these filter media can be to convert carbonate from ureahydrolysis to bicarbonate. Such cation exchange materials can includezirconium phosphate, titanium phosphate, or zeolite. Anion exchangefilter media bind phosphate, fluoride, and other heavy metals.By-products of the anion exchange filter media can include acetate andbicarbonate, which also corrects for metabolic acidosis of a patient'sblood. Such filter media can include hydrous zirconium oxide of theacetate form, hydrous silica, stannic oxide, titanium oxide, antimonicacid, hydrous tungsten oxide, or sodium zirconium carbonate.

The present invention relates in part to a method of synthesizingzirconium phosphate particles by a sol gel technique using a solution ofzirconium oxychloride in which the hydration of zirconium ions in thesolution has been reduced. This can be accomplished, for example, by theuse of an additive or additives in the zirconium oxychloride solution tochange the zirconium ions in the solution from a highly hydratedmonomeric form to a soluble polymeric zirconium complex with a highnumber of polymer units and a reduced water of hydration.

The present invention relates to a method of making zirconium phosphateparticles comprising: (a) combining at least one low molecular weight,oxygen containing, monofunctional, organic additive with zirconiumoxychloride in an aqueous solvent to form a solution wherein the lowmolecular weight, oxygen containing, monofunctional, organic additiveforms a complex with zirconium ions in the solution, and (b) combiningthe solution obtained in (a) with phosphoric acid and evaporating thelow molecular weight, oxygen containing, monofunctional, organicadditive to obtain zirconium phosphate particles by sol gelprecipitation. As typical, non-limiting amounts, the at least one lowmolecular weight, oxygen containing, monofunctional, organic additivecan be present in an amount of from about 20 wt % to 70 wt % by weightof the zirconium oxychloride (e.g., 25 wt % to 60 wt %, 30 wt % to 50 wt% additive) and/or the molar ratio of zirconium oxychloride tophosphoric acid can be from 1:2.8 to 1:3.2. Other amounts and molarratios below and above these ranges can be used. The aqueous solvent canbe deionized water or reverse osmosis (RO) water. The zirconiumoxychloride can be dissolved (or otherwise mixed) in the aqueous solventand then the low molecular weight, oxygen containing, monofunctional,organic additive can be added to form the solution of step (a). Thezirconium oxychloride can be dissolved (or otherwise mixed) in theaqueous solvent and then the low molecular weight, oxygen containing,monofunctional, organic additive can be added to form the solution ofstep (a). The zirconium oxychloride can be present in the aqueoussolvent up to a saturation concentration or other concentration levels.The low molecular weight, oxygen containing, monofunctional, organicadditive can be dissolved (or otherwise mixed) in the aqueous solventand then the zirconium oxychloride can be added to form the solution ofstep (a). The low molecular weight, oxygen containing, monofunctional,organic additive can be present in the solution of step (a) in a molaramount sufficient so that all or substantially all of the zirconium ionsin the solution are converted to a complex. The low molecular weight,oxygen containing, monofunctional, organic additive can form a solublepolymer complex with zirconium ions.

To explain how a low molecular weight, oxygen containing,monofunctional, organic additive can affect the characteristics ofzirconium phosphate formed in a sol gel process, it helps to understandthe nature of the zirconium ions in a zirconium oxychloride solution inthe absence of an additive. Zirconium ions in a zirconium oxychloridesolution by itself are highly hydrated zirconium species with 4-8molecules of H₂O coordinated with each zirconium (Zr) atom. The hydratedions can form polymeric units ranging from a monomer, ZrOOH⁺, to atetramer, Zr₄(OH)₈ ⁺⁸, depending on the concentration of the solution.As phosphoric acid is mixed with a zirconium oxychloride solution atroom temperature, a sol gel zirconium phosphate precipitate is formed ata very rapid rate, trapping a large number of coordinated watermolecules (or hydronium ions since the lattice H⁺ can combine with H₂Omolecules to form H₃O⁺) within the gel particle to form a soft gel. Asdiscussed above, these soft gel particles can have a tendency toagglomerate as the slurry gets denser and when the material is packed ona filter during filtration or on trays during drying.

Using at least one low molecular weight, oxygen containing,monofunctional, organic additive preferably forms new zirconiumpolymeric species in solution having a reduced number of coordinatedwater molecules and a high polymer unit so that when these zirconiumpolymeric species react with phosphoric acid, the problems describedabove that arise from excessive hydration do not occur. In particular,the reaction of zirconium ions with phosphate is slowed, which allowsfor the concentration of reactants to be more easily controlled, therebyallowing for the particle size and/or particle size distribution of theparticles formed by precipitation to be controlled. Because of thereduced water content, the particles formed by precipitation are harderand/or less prone to agglomeration and/or have a more refined molecularstructure. If the low molecular weight, oxygen containing,monofunctional, organic additive that is used also has properties of anemulsifying agent, it is possible to improve the shape of the particlesformed by precipitation from irregular to roughly or nearly spherical orspherical. Doing so may reduce or eliminate the agglomeration problemduring drying, allowing for the formation of a free-flowing powder. Evenif the particle size is kept small, the flow performance for columnapplication can be improved. Except as otherwise provided herein, thesynthesis of zirconium phosphate particles by the sol-gel process can becarried out according to known sol-gel techniques. For example, theaqueous solution used to initially dissolve the zirconium oxychloridecan be water purified to remove ionic impurities such as trace metals byreverse osmosis (RO water) or by any other method that provides a lowenough level of contaminants to be acceptable for the intended end useof the zirconium phosphate particle or can be deionized water. Forcarrying out the sol-gel precipitation, either phosphoric acid or a saltsolution of phosphate can be used. At a high pH (e.g., about 4 pH orabove), the use of a phosphate salt results in a product with a reducedammonium capacity. Reference to phosphoric acid can includeorthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid,tetrapolyphosphoric acid, trimetaphosphoric acid, and/or phosphoricanhydride, or combinations thereof. The phosphoric acid can have amolarity of 1 mole/L or higher, for instance, 1.5 moles/L to 3 moles/L,or 2.6 to 2.8 moles/L.

The low molecular weight, oxygen containing, monofunctional, organicadditive used in the present invention can be capable of displacingwater molecules that are coordinated to zirconium ions in an aqueoussolution of zirconium oxychloride and that can preferably bridgezirconium ions to form a water soluble polymer species. More than onetype of additive can be used, e.g., mixtures. The additive can beselected so that it can be displaced from the zirconium ions during thereaction with phosphoric acid or phosphate that forms zirconiumphosphate. The additive can lead to the formation of polymer speciesthat are preferably soluble in water. Accordingly, additives that arepreferred in the present invention include alcohols and/or carboxylicacids comprising a single functional group (i.e., monofunctional), thatare soluble in water. For purposes of this invention, a monofunctionalcompound can be an organic compound whose chemical structure possesses asingle reactive site (e.g., a single reactive —OH group).

Examples of low molecular weight, oxygen containing, monofunctional,organic additives that can be used in the present invention includealcohols having the following formula: R—OH, wherein R is a C₁₋₆ alkylgroup, preferably a C₁₋₃ alkyl group, and carboxylic acids having thefollowing formula: R—COOH, wherein R is a C₁₋₆ alkyl group, preferably aC₁₋₃ alkyl group. The alcohol and carboxylic acids can be non-branchedor branched isomers. Specific, non-limiting examples of additives thatcan be used are methanol, ethanol, propanol, isopropanol, acetic acid,propionic acid, or combinations thereof. Examples of low molecularweight include, but are not limited to, a molecular weight of about20-80, preferably about 30-60.

Typical examples of low molecular weight, oxygen containing,monofunctional, organic additives and the zirconium polymer complexformed in a zirconium oxychloride solution are as follows:

Alcohol ROH

Carboxylate or carboxylic acid RCOOH

A solution wherein the low molecular weight, oxygen containing,monofunctional, organic additive forms a complex with zirconium ions canbe formed by adding the additive to a solution containing zirconiumoxychloride or by adding zirconium oxychloride to a solution containingthe additive. In other words, the order of addition of the additive andthe zirconium oxychloride to an aqueous solvent is not critical.

The properties of zirconium phosphate particles obtained by sol gelprecipitation can optionally be altered by adjusting the pH of thephosphoric acid solution used. For example, the precipitating agent usedin the method of the present invention can be orthophosphoric acid thatis titrated with a base, like NaOH, to a pH of from about 1 to about 4.The partially titrated phosphoric acid can lower the acidity of the solgel ZrP and thereby reduce the water of hydration. Otherwise, lattice H⁺can combine with H₂O to form hydronium ions. Thus, carrying out sol gelprecipitation at a higher pH of phosphate helps to promote the hardeningof the ZrP gel. However, carrying out the precipitation reaction at analkaline pH is less preferred because zirconium phosphate precipitatedby alkaline phosphate can have poor ammonia adsorption properties. Thistechnique can be carried out in conjunction with the use of at least onelow molecular weight, oxygen containing, monofunctional, organicadditive, as described above.

The present invention also relates in part to a method of synthesizingzirconium phosphate particles by sol gel precipitation wherein theparticle size and/or particle size distribution of the zirconiumphosphate particles obtained are controlled by controlling the rate atwhich the organic additive-containing solution of zirconium oxychlorideis added to the reaction vessel, the rate at which the solution ofphosphoric acid is added to the reaction vessel, the concentration ofreactants, e.g., zirconium oxychloride, organic additive, phosphoricacid, and/or hydrochloric acid in the reaction vessel, and/or the speedand manner of agitation of the reaction mixture. In particular, it hasbeen found that the particle size obtained by sol gel precipitation canbe partly dependent upon the concentration of the reactants. When asolution of zirconium oxychloride is added to a solution of phosphoricacid, the concentration of phosphoric acid decreases as the reactionproceeds, leading to the possible formation of increasingly smallerparticles. As a result, an undesirably wide range of particle sizes maybe produced. To prevent this from possibly happening, both reactants,i.e., the additive-containing solution of zirconium oxychloride, andphosphoric acid, can optionally be added to a reaction vesselsimultaneously (or nearly simultaneously) and the addition can bestretched out over a period of time, such as, for example, ten to thirtyminutes or more, thereby allowing the concentration of phosphoric acidin the reaction solution to remain steady and controllable throughoutthe precipitation process. As a further example, a portion of a solutionof phosphoric acid can be added to a reaction vessel, and theadditive-containing solution of zirconium oxychloride and the remainderof the phosphoric acid solution can be added to the reaction vesselsimultaneously at controlled rates, again allowing the concentration ofphosphoric acid in the reaction solution to remain steady andcontrollable throughout the precipitation process.

In addition to the simultaneous addition of zirconium oxychloride andphosphoric acid solutions, other parameters, including the manner ofaddition of the zirconium oxychloride solution and the manner of mixingof the reactants, can be controlled to provide a more efficient reactionand to control the particle size range. For example, a spray head can beused as the inlet for the additive-containing solution of zirconiumoxychloride so that the solution is added to the reaction vessel in theform of droplets, thereby providing a more efficient reaction. Further,the reaction vessel can be equipped to agitate the reactants as they areadded to the reaction vessel and as the reaction proceeds, therebyproviding for more efficient mixing and avoiding differences in particlesizes caused by differing concentrations of reactants in differentsections of the reaction vessel. For example, the reaction vessel caninclude an agitator, such as, for example, an agitator having more thanone set of blades attached to a shaft at different levels, so that thereactants in the reaction vessel are thoroughly mixed at all levels. Asa particular example, a multi-impeller agitator can be used, such as anagitator that has three sets of blades, each set attached to a shaft ata different level. The use of an agitator to control or reduceagglomeration is optional. If an agitator is used, commercial agitators,including multi-impeller agitators, can be used. With a multi-impelleragitator, a low agitation speed, such as, for example 20-40 rpm, ispreferred to avoid agglomeration without causing a break-up of gelparticles. With a single-impeller agitator, a speed of about 60-70 rpm,for example, can be used. For any given agitator, the optimum speed isdependent on variables such as the tank size, shape, baffles, impellersize, and the like. Other methods of agitation or mixing can be used.

Appropriate process control methods can be used to ensure a suitableconcentration range of reactants and flow rates for the precipitationprocess so that a desirable particle size range or distribution can beobtained. As an example, a desirable particle size range for zirconiumphosphate particles to be used in a sorbent dialysis cartridge can befrom about 20-80 microns, or from about 35-65 microns. Other particlesize ranges can be used. To achieve this particle size distribution, andas an example, zirconium oxychloride solution containing isopropanol anda phosphoric acid solution can be formed as follows. The zirconiumoxychloride solution can contain zirconium oxychloride at, or close to,its saturation point (for example, 500 g ZOC crystals in 375 mL water)since the size of polymeric units increases as the concentrationincreases. The amount of isopropanol can be the maximum amount (forexample, about 300 g in the ZOC solution described herein) to providethe maximum reduction in the amount of coordinated water in thezirconium ion complex and suppress the degree of gelation. An excessamount of isopropanol can reduce the particle size too much by excessiveemulsification, thereby producing many fine particles. An insufficientamount of isopropanol can result in an elevated degree of agglomerationand a higher percentage of particles in the larger size range (e.g.,80-120 microns). A typical solution of phosphoric acid can contain 516.5g of 76% H₃PO₄+2.1 L water. The molar ratio of ZOC to phosphate or H₃PO₄can be about 1:3±0.2.

A specific non-limiting example of a ZOC solution formulation is 500 gZOC, 375 g water, 300 g isopropanol, and 70 g concentrated HCl. Themolar ratio of ZOC to water to low molecular weight, oxygen containing,monofunctional, organic additive can be about 1:0.75:0.6. Anotherspecific non-limiting example of a ZOC solution formulation is 500 gZOC, 375 g water, 260 g glacial acetic acid, and 94 g concentrated HCl.The molar ratio of ZOC to water to low molecular weight, oxygencontaining, monofunctional, organic additive can be about 1:0.75:0.52.The amounts given for the typical solution can, of course, be scaled upor down by maintaining the same proportion of reactants. Particle sizecontrol for use in sorbent dialysis cartridges can also be achieved byadditional milling, if necessary, to meet cartridge performancerequirements.

The flow rate for the phosphoric acid solution can be 80-100 ml/min foran addition time of 25-30 minutes, and the flow rate of theadditive-containing solution of zirconium oxychloride can be 25-50ml/min for an addition time of 15-30 minutes. The flow rate is providedfor the solution described above and can be scaled up or down if adifferent amount of reactants is used. A higher flow rate of thephosphoric acid can increase its steady state concentration in thereaction bath and/or produces harder stable crystalline ZrP particles.Conversely, a lower flow rate can produce a more fragile product. As aspecific example, the addition time of the reactants can be 30 minutes.Other flow rates and times can be used.

The sol gel zirconium phosphate particles in a slurry formed by a methodaccording to the present invention can be stabilized by an immediatetitration to raise the pH of the slurry. For example, the slurry can betitrated with a base, such as 50% NaOH, to bring the pH up to a range ofabout 1-2. (Typically, the pH of the slurry when formed is close to 0.1)Then, after allowing the zirconium phosphate particles to settle andharden further, the slurry can be titrated slowly to a higher pH, suchas pH 5.5 or pH 6 to obtain the finished product. The partial titrationprovides an immediate reduction in the acidity of the material, whichmay otherwise induce the adsorption of water of hydration (since latticeH⁺ can combine with H₂O to form hydronium ions) and a softening of thegel. The advantage to performing the titration slowly and in stages isthat the rapid addition of alkali can cause the rapid formation of waterwithin the gel particles, which can burst the particles and produce anexcessive number of fines. For the specific use of zirconium phosphateparticles in sorbent dialysis cartridges, the second titration ispreferable to a pH of 5.5 to obtain the optimum Na⁺ content in theproduct due to the presence of Na⁺ and PO₄ ions already present in theslurry.

Because sol gel precipitation in the phosphate concentration range usedin the present invention tends to be a fast reaction, the techniquesdescribed above can be carried out without additional heating. However,a thermal treatment carried out with water may be helpful to improve themolecular structure of the zirconium phosphate particles by enhancingcrystallinity. Thermal treatment may improve the crystal structure ofZrP by promoting an oxolation reaction as follows

and by aiding the release of ionic impurities from the zirconiumphosphate lattice formed in the sol gel precipitation. As an example ofhow the thermal treatment can be carried out, after zirconium phosphatehas been formed by sol gel precipitation, the reaction slurry can befiltered and washed to remove chloride, excessive phosphoric acid,sulfate and additive chemicals. The filter cake obtained by filtrationcan then be transferred to a bath of deionized water (or RO water) andthe slurry can be agitated for a short time (first wash). The filtrationand washing can be repeated, for instance, until the total dissolvedsolids level (TDS level) in slurry is below 1200 ppm. The filter cakecan be transferred to a bath of deionized water (or RO water) in aheating vessel equipped with an agitator and, with a moderate agitationspeed, the slurry can be heated at moderate rate to about 180-185° F.(about 82-85° C.) with the temperature maintained in this range for 1hour or longer. Then, the heated slurry can be allowed to cool to roomtemperature and the volume can be adjusted with water. Thereafter, theslurry can be titrated from a starting pH of about 1.8 to a desired pH,such as a pH of 5.75; pH 6; or pH 6.25 (or ranges therebetween) with abase, such as 50% NaOH, to obtain ZrP products of different Na⁺ contentsand acidity. The titrated ZrP can then be washed and filtered repeatedlywith deionized water (or RO water) until the TDS level in the slurry isbelow 500 ppm. The filter cake after the final wash can then betransferred to a tray dryer and the titrated product can be dried to14-18% loss on drying by moisture balance (LOD) at a temperature ofabout 160°-180° F. (71°-81° C.). The final product can be in the form offree-flowing powder, for instance, in a target particle size range of30-60 μm and can be without agglomeration (or less than 1% by weight).

The following examples are given to illustrate the nature of theinvention. It should be understood, however, that the present inventionis not to be limited to the specific conditions or details set forth inthese examples.

EXAMPLES Example 1 Preparation of ZrP Particles by Sol Gel Precipitation

Solution A was prepared as follows: 20 g ZOC crystals was dissolved in15 ml deionized water and 15 ml isopropanol was added to the solution.Then, with agitation by magnetic stirrer or plastic impeller, about 100drops of concentrated HCl was added to the solution with continuedagitation until all precipitate was redissolved to form a clearsolution.

Solution B was prepared as follows: 30 g Technical Grade phosphoric acid(76%) was diluted in 60 ml water in a 500 ml beaker. With a magneticstirrer, the diluted acid was heated to a boiling temperature.

Reaction process steps:

-   -   Step 1: Solution A was pumped into Solution B at boiling        temperature at about 10 ml/min flow rate, with moderate        agitation speed using magnetic stirrer or plastic impeller.    -   Step 2: After addition was complete to produce a slurry of        precipitate, the slurry was heated for one hour to evaporate off        the alcohol completely and improve crystal structure of the AZP        precipitate.    -   Step 3: After heating for one hour, the slurry was allowed to        cool. The precipitate was then filtered and washed with        deionized water to remove excessive unreacted phosphoric acid.    -   Step 4: The washed product was dried in an oven at 180° F. until        the moisture level was 5-20 weight percent LOD to form a        free-flowing powder. The particle size was in a range of from        25-45 microns.

Example 2

Example 1 was repeated but the acid zirconium phosphate (AZP) productwas titrated to pH 6.0 with 50% NaOH in about 200 ml deionized water andfollowed by washing before filtration and drying of the filteredproduct.

Example 3

The mixing process of ZOC/isopropanol and phosphoric acid in Example 1was performed again at the ambient temperature of the acid. The NH₄ ⁺—Nadsorption capacity of the final product was about the same as theproduct obtained by high temperature mixing although there was somedegree of agglomeration upon drying of the product.

Example 4

ZrP with particle size in the range 2-10 microns was obtained bygrinding the final dried product of Example 1 or by modifying theformulation of the ZOC solution as follows before adding to the heatedphosphoric acid and mixing with vigorous agitation:

ZOC solution formulation (Solution A): ZOC solid 20 gm Deionized water15 ml Isopropanol 30 ml Conc. HCl  0 drops

The NH₄ ⁺—N adsorption capacity of the fine particle size product wasfound to increase by about 10-20% over that of the normal particle sizerange (25-65 microns).

Example 5

A scale-up batch for Example 1 was made by adjusting the solutionformulations (Solution A and Solution B) and the process parameters wereas follows:

Solution A ZOC solid 500 gm Deionized water 375 ml Isopropanol 375 ml or300 gm Conc. HCl  70 gm Solution B 76% H₃PO₄ 550 gm Deionized water  2.2L (NOTE: Molar mixing ratio of ZOC:H₃PO₄ = about 1:2.92)

Reaction process steps:

-   -   Step 1: Solution A was pumped into Solution B at boiling        temperature at about 25-30 ml/min flow rate for an addition time        of 25-30 minutes, with moderate agitation speed (about 80 RPM)        using plastic impeller.    -   Step 2: After addition was complete to produce a slurry of        precipitate, the slurry was heated for 30 minutes to evaporate        the alcohol completely and improve the crystal structure of the        AZP precipitate.    -   Step 3: After heating for 30 minutes, the slurry was allowed to        cool. The precipitate was then filtered and washed with        deionized water to remove excessive unreacted phosphoric acid.    -   Step 4: The filter cake was transferred to about 3 L deionized        water and agitated at mild speed to form a slurry, which was        then titrated to a pH 6.0 by 50% NaOH. The titrated ZrP was then        filtered and rewashed until the TDS in filtrate was about 500        PPM.    -   Step 5: The washed product was dried in an oven at 180° F. until        the moisture level was about 5-20 weight percent LOD to form a        free-flowing powder. The particle size was in the range of 35-65        microns.

The NH₄ ⁺—N adsorption capacity of the product was the same as the smallsample test in Example 1.

Example 6

Example 1 was repeated using acetic acid as organic additive in place ofisopropanol with the ZOC solution formulation as follows (Solution A):

ZOC solid  20 gm Deionized water  15 ml Glacial acetic acid  15 ml Conc.HCl 200 drops

The same amount and concentration of phosphoric acid at boilingtemperature were used as in Example 1. The product was excessivelywashed with deionized water to remove residual acetic acid then titratedto pH 6.0. The same particle size ZrP product (35-65 microns) withoutagglomeration upon drying was obtained although NH₄ ⁺—N adsorptioncapacity was slightly lower than that made by using isopropanol.

Example 7

Example 6 was repeated but the ZOC/acetic acid solution (Solution A) wasadded to the phosphoric acid at ambient temperature. The product wasexcessively washed with deionized water to remove residual acetic acid.One-half of the product was titrated to pH 6.0 while the other halfremained untitrated. It was shown that all ZrP products had the same NH₄⁺—N adsorption capacity as Example 6 regardless of mixing temperatureand pH titration of product although the product obtained at ambienttemperature of mixing had some degree of agglomeration upon drying.

Example 8

A scale-up batch for Example 7 at ambient temperature of mixing was madeby adjusting the solution formulations (Solution A and Solution B) asfollows:

Solution A ZOC solid 500 gm Deionized water 375 ml Glacial acetic acid250 ml or 260 gm Conc. HCl  94 gm Solution B 76% H₃PO₄ 550 gm Deionizedwater  2.2 L (NOTE: Molar mixing ratio of ZOC:H₃PO₄ = about 1:2.92)

An excessive amount of water was used to wash the product to removeresidual acetic acid. The NH₄ ⁺—N adsorption capacity of the titratedproduct was about the same as the small sample test in Example 7although the product obtained at ambient temperature of mixing had somedegree of agglomeration upon drying.

Example 9

The fine particle ZrP with particle size in the range 2-10 microns wasobtained by grinding the final dried product of Example 6 or bymodifying the formulation of the ZOC solution as follows before addingto the heated phosphoric acid and mixing with vigorous agitation:

ZOC solution formulation (Solution A): ZOC solid 20 gm Deionized water15 ml Glacial acetic acid 30 ml Conc. HCl  0 drops

The NH₄ ⁺—N adsorption capacity of the fine particle size product wasfound to increase by about 10-20% over that of the normal particle sizerange (25-65 microns).

Example 10 ZrP Particles Having Enhanced Ammonium Adsorption Capacity

ZrP particles were prepared by a sol gel method according to the presentinvention, by the sol gel method according to U.S. Patent ApplicationPublication No. 2006/0140840 (Example 2 using glycerol and sodiumsulfate as the additive), and from basic zirconium sulfate (BZS) by a(non-sol gel) method prepared as follows: one (1) kg of BZS was added todeionized water in a reactor to form a slurry with moderate agitationspeed. Then, about 770 ml Technical Grade phosphoric acid (76%) dilutedwith equal volume of water was pumped into the slurry. With slowagitation, the slurry was heated at moderate or maximum rate to 180-185°F., and then heated to maintain that temperature for one hour after thetemperature was reached. The slurry was then cooled to room temperature.The product was filtered and washed in a Buchnell funnel with deionizedwater. The filter cake was then dried in a tray dryer at 180° F. untilthe moisture level was 12-18 weight percent LOD. The particle size wasin a range of from 25-60 microns.

The NH₄ ⁺—N adsorption capacity was measured at three NH₄ ⁺—N exposedconcentrations and the results were compared. The results, shown inTable 1, confirm that ZrP particles prepared according to the presentinvention exhibit increased NH₄ ⁺—N adsorption compared to particlesprepared by the previous methods.

TABLE 1 NH₄ ⁺—N adsorption Exposed NH₄ ⁺—N per g ZrP (capacity in Typeof ZrP concentration presence of Na) Capacity in Water Sol gel ZrPaccording to  5 mg/dL 4.95 mg NH₄ ⁺—N/g present invention 10 mg/dL 7.76mg NH₄ ⁺—N/g 25 mg/gm (Example 1) 20 mg/dL 11.84 mg NH₄ ⁺—N/g  38 mg/gmSol gel ZrP according to  5 mg/dL 2.23 mg NH₄ ⁺—N/g U.S. PatentApplication 10 mg/dL 3.74 mg NH₄ ⁺—N/g Publication No. 20 mg/dL 7.60 mgNH₄ ⁺—N/g 2006/0140840 ZrP made from BZS  5 mg/dL 2.00 mg NH₄ ⁺—N/g 10mg/dL 3.58 mg NH₄ ⁺—N/g 20 mg/dL 6.515 mg NH₄ ⁺—N/g 

Example 11

Grinding the ZrP product (e.g., ZrP of Example 1) to fine particle sizeafter drying can increase the NH₄ ⁺ adsorption capacity from 28 mg NH₄⁺—N/gm to 36 mg NH₄ ⁺—N/gm at the NH₄ ⁺—N concentration of 20 mg/dL inwater (˜28%). The adsorption isotherms after grinding in comparison withZrP made from BZS can be shown by the Table below:

TABLE 2 NH₄ ⁺—N Capacity in the concentration NaHCO₃/NaCl dialysateAdsorption isotherm Sol gel ZrP 10 mg/dL   8 mg/gm NH₄ ⁺—N adsorption 20mg/dL 11.3 mg/gm capacity (mg/gm ZrP) = 55 mg/dL   15 mg/gm 7.16 + 0.15× [NH₄ ⁺—N] 85 mg/dL   19 mg/gm r = 0.9878 100 mg/dL    23 mg/gm CurrentZrP 10 mg/dL  4.2 mg/gm NH₄ ⁺—N adsorption made from BZS 20 mg/dL 7.12mg/gm capacity (mg/gm ZrP) = 55 mg/dL 10.2 mg/gm 3.38 + 0.137 × [NH₄⁺—N] 85 mg/dL 15.4 mg/gm r = 0.99 100 mg/dL  17.1 mg/gm

Other typical NH₄ ⁺—N adsorption capacity data in water in variationwith organic additives (isopropanol, acetic acid, tartaric acid,glycerol, polyvinyl alcohol); temperature of mixing (ambient vs. boilingtemperature); ZrP pH (ZrP pH 6.0 vs. untitrated ZrP); and particle size(35-65 microns vs. ground ZrP fine powder, 2-10 microns) are summarizedin the Table as shown below: (NOTE: Moisture level data was not takenbecause it is found that sol gel ZrP can be dried to very low moisturelevel without affecting the NH₄ ⁺—N adsorption capacity).

TABLE 3 Temperature NH₄ ⁺—N adsorption capacity in water Organicadditive of mixing ZrP pH Particle size mg/gm ZrP Isopropanol ambientuntitrated ground ZrP fine powder at 10 mg/dL NH₄ ⁺—N conc. 28.89 mg/gm2-10 microns at 20 mg/dL NH₄ ⁺—N conc. 36.21 mg/gm boiling untitratedground ZrP fine powder at 10 mg/dL NH₄ ⁺—N conc. 26.9 mg/gm 2-10 micronsat 20 mg/dL NH₄ ⁺—N conc. 34.76 mg/gm boiling untitrated 35-65 micronsat 10 mg/dL NH₄ ⁺—N conc. 25.53 mg/gm at 20 mg/dL NH₄ ⁺—N conc. 31.83mg/gm boiling pH 6.0 ground ZrP fine powder at 10 mg/dL NH₄ ⁺—N conc.24.9 mg/gm 2-10 microns at 20 mg/dL NH₄ ⁺—N conc. 38.4 mg/gm boiling pH6.0 35-65 microns at 10 mg/dL NH₄ ⁺—N conc. 24.66 mg/gm at 20 mg/dL NH₄⁺—N conc. 32.19 mg/gm boiling pH 4.0 35-65 microns at 10 mg/dL NH₄ ⁺—Nconc. 27.54 mg/gm at 20 mg/dL NH₄ ⁺—N conc. 33.45 mg/gm acetic acidambient untitrated ground ZrP fine powder at 10 mg/dL NH₄ ⁺—N conc.25.95 mg/gm 2-10 microns at 20 mg/dL NH₄ ⁺—N conc. 35.7 mg/gm ambientuntitrated 35-65 microns at 10 mg/dL NH₄ ⁺—N conc. 24.96 mg/gm at 20mg/dL NH₄ ⁺—N conc. 27.3 mg/gm ambient pH 6.0 35-65 microns at 10 mg/dLNH₄ ⁺—N conc. 25.65 mg/gm at 20 mg/dL NH₄ ⁺—N conc. 28.95 mg/gm boilingpH 6.0 35-65 microns at 10 mg/dL NH₄ ⁺—N conc. 25.45 mg/gm at 20 mg/dLNH₄ ⁺—N conc. 26.64 mg/gm no organic ambient untitrated ground ZrP finepowder at 10 mg/dL NH₄ ⁺—N conc. 21.47 mg/gm additive; just conc. 2-10microns at 20 mg/dL NH₄ ⁺—N conc. 27.31 mg/gm HCl alone (partialgelation) Boiling pH 6.0 35-65 microns at 10 mg/dL NH₄ ⁺—N conc. 20.27mg/gm at 20 mg/dL NH₄ ⁺—N conc. 24.2 mg/gm Glycerol Boiling pH 6.0 35-65microns at 10 mg/dL NH₄ ⁺—N conc. 6.46 mg/gm at 20 mg/dL NH₄ ⁺—N conc.9.98 mg/gm polyvinyl alcohol Boiling pH 5.0 35-65 microns at 10 mg/dLNH₄ ⁺—N conc. 3.92 mg/gm at 20 mg/dL NH₄ ⁺—N conc. 5.39 mg/gm tartaricacid Boiling pH 6.0 35-65 microns at 10 mg/dL NH₄ ⁺—N conc. 2.76 mg/gmat 20 mg/dL NH₄ ⁺—N conc. 3.43 mg/gm

Example 12

A lab-scale parametric study of the sol gel process for preparation ofZrP particles was performed for various parameters, including, forexample, type and amount of additive to ZOC solution, reactant mixingmethod, phosphoric acid amount, hydrothermal treatment of crude sol gel,HCl amount, and particle size. Comparison gels comprising ZrP preparedwith an inorganic oxygen additive (Na₂CO₃ (soda ash)), and ZrP made fromBZS, were included in this study. Some of the product particles wereanalyzed for one or more of adsorption capacity, BET surface area, porevolume, pore size distribution, and/or gel swelling property. Forpurposes of this example, reverse osmosis (RO) water can be substitutedfor deionized (DI) water where referenced.

Method Steps:

Step 1: Preparation of ZOC Solution with Additive (Solution A)

Solution A was prepared with an additive selected from alcohol(isopropanol or 95% methanol), acetic acid, or soda ash. These types ofsolutions are designated Solutions A1, A2, and A3.

Solution A1 was prepared as follows: 500 g ZOC crystals was dissolved in375 ml deionized (DI) water with agitation, and 200 ml glacial aceticacid is transferred to the ZOC solution and agitated until the solutionmixture was completely clear. (NOTE: About 50 gm conc. HCl optionallycan be added to the ZOC solution first before the mixing with aceticacid if a larger particle size is desired. Agitation to re-dissolve anyprecipitate thus formed until the solution is clear).

Solution A2 was prepared as follows: 500 g ZOC crystals was dissolved in375 ml deionized water with agitation, and 300 ml (isopropanol or 95%methanol) is transferred to the ZOC solution and agitated until thesolution mixture was completely clear. (NOTE: Addition of conc. HCL toimprove particle size is optional as in Solution A1).

Solution A3 was prepared as follows: 500 g ZOC crystals was dissolved in250 ml deionized water with agitation (totally or partially), and 40 gsoda ash was dissolved in 125 mL deionized water in another vessel withagitation (totally or partially). The soda ash solution (totally orpartially dissolved) was transferred to the ZOC solution and agitateduntil the solution mixture is completely clear. (NOTE: Addition of conc.HCl also is optional as in Solutions A1 and A2). The resultant solutionwas used at once or within a short time for the sol gel ZP synthesis.

Step 2: Preparation of Phosphoric Acid Used for Reaction (Solution B)

Solution B was prepared as follows: 600 g Technical Grade phosphoricacid (76%) was diluted in 500 deionized mL water and mixed withagitation.

Step 3: Precipitation Reaction of Sol Gel ZP by Simultaneous Addition ofZOC and H₃PO₄

a) Approximately 280 ml of the diluted phosphoric acid prepared in Step2 was transferred to a 4 L reactor vessel and agitation was started at240 RPM.

b) Solution A and Solution B were simultaneously pumped into the reactorvessel at ambient temperature at the flow rate of about 20 mL/min forboth fluids such that the addition of the two fluids was completesimultaneously after about 30 minutes.

c) 500 mL deionized water was added to dilute the slurry and theagitation was continued until the sol gel ZP particles hardened.

Step 4: Washing of Crude Sol Gel ZP

The slurry of product from Step 3 was pumped into a vacuum batch filterand the filter cake was briefly washed with 6 L deionized water toremove the chloride. (NOTE: If hydrothermal treatment is not used in thefollowing Step 5, Step 4 goes directly to removal of excessive PO₄ forpre-titration in Step 6 by continuing to wash the filter cake until thefiltrate has TDS below 1200 ppm).

Step 5: Hydrothermal Treatment

The washed filter cake obtained from Step 4 was transferred into 3 Ldeionized water in the 4 L reactor vessel, and agitated at slow speed toform a slurry. 150 g 76% H₃PO₄ was added to the slurry and the resultingslurry was heated to a temperature at about 90° C., and maintained atthat temperature or just below that temperature for one hour and thenheating was stopped to allow the slurry to cool.

Step 6: Filtration/Washing to Remove Excessive PO₄ for Pre-Titration

The cooled slurry of Step 5 was pumped after the hydrothermal treatmentto the vacuum batch filter. The filter cake was washed with deionizedwater until the filtrate has TDS below 1200 ppm.

Step 7: Filtration of Acid Sol Gel ZP

The acid sol gel ZP filter cake was transferred after washing to a 6 Lbath of deionized water and agitated mildly to form a slurry. The slurrywas titrated to pH 6 by adding 50% NaOH.

Step 8: Final Washing and Drying

The slurry of Step 7 was pumped after titration to the vacuum batchfilter. The washing of the filter cake was continued until the TDS ofthe filtrate is below 500 ppm. The filter cake was transferred to a traydryer and the material was dried at a temperature of 100° F.-120° F. tothe moisture level of 18-22% LOD. Continuous stirring of the materialduring drying was used to ensure uniform drying.

Step 9: Particle Size Control

The dried product was gently ground to a free-flowing powder to break upthe soft agglomerates. The powder product was sieved and the portion waskept with the particle size in the ranges (45-90) microns or (45-180)microns for testing.

Product quality-material testing: NH₄ ⁺—N adsorption quality

The NH₄ ⁺—N adsorption quality of the sol gel ZP samples were testedaccording to the procedure as follows:

1 gm of sample was shaken in 300 ml of (NH₄)₂CO₃ solution in deionizedwater for 5 minutes at concentrations of (a) 20 mg/dL NH₄ ⁺—N; (b) 30mg/dL NH₄ ⁺—N. (NOTE: Some sample tests were repeated by using (NH₄)₂CO₃solution in dialysate (105 mEq/L NaCl; 35 mEq/L NaHCO₃). Filtering withWhatman #42 was done afterwards and residual NH₄ ⁺—N concentration wasanalyzed by Indophenate Test to calculate adsorption capacity of thesample.

The results for NH₄ ⁺—N adsorption quality determinations for varioussol gel ZP samples representing embodiments of the present invention andcomparison or control sol gel ZP samples are indicated in Table 4. Table4 comprises the indicated parts 4A-4J. “Mic” is microns.

TABLE 4 Parameters Adsorption Quality Method of Particle HydrothermalConc. 75% Sample Capacity at NH₄ ⁻N conc. Of Additive Mixing SizeTreatment HCl H₃PO₄ No. 20 mg/dL 30 mg/dL 4A: Parametric Variation:Simultaneous Addition of ZOC and H₃PO₄ 375 ml Simultaneous <200 mic  Nohydrothermal treatment 50 gm 600 gm  1 39.16 mg per gm 41.15 mg per gmisopropanol add >45 mic 375 ml Simultaneous <200 mic Hydrothermaltreatment with 50 gm 600 gm  2 35.84 mg per gm 38.13 mg per gmisopropanol add >45 mic 100 gm phosphoric acid (overdried 11.6% LOD) 375ml Simultaneous <200 mic Hydrothermal treatment with 50 gm 600 gm  338.53 mg per gm 42.21 mg per gm isopropanol add >45 mic 100 gmphosphoric acid 240 ml acetic Simultaneous <90 mic Hydrothermaltreatment with 50 gm 600 gm  4   40 mg per gm 43.23 mg per gm acidadd >45 mic 100 gm phosphoric acid  5 39.31 mg per gm 44.26 mg per gm375 ml Simultaneous <90 mic No hydrothermal treatment 50 gm 600 gm  6  40 mg per gm 45.26 mg per gm isopropanol add >45 mic 300 ml aceticSimultaneous <90 mic No hydrothermal treatment 50 gm 600 gm  7 36.42 mgper gm 44.31 mg per gm acid add >45 mic 375 ml Simultaneous <90 mic Nohydrothermal treatment 50 gm 600 gm  8 35.29 mg per gm 41.21 mg per gm95% methanol add including fines 375 ml Simultaneous <90 micHydrothermal treatment with 50 gm 600 gm  9 37.48 mg per gm 45.36 mg pergm 95% methanol add >45 mic 150 gm phosphoric acid 150 ml aceticSimultaneous <90 mic No hydrothermal treatment 50 gm 600 gm 10 37.56 mgper gm 43.45 mg per gm acid add >45 mic 150 ml 95% Simultaneous <90 micNo hydrothermal treatment 50 gm 600 gm 11 34.611 37.91 mg per gmmethanol add >45 mic mg per gm 150 ml 95% Simultaneous <90 mic Nohydrothermal treatment 50 gm 500 gm 12  32.9 mg per gm  42.2 mg per gmmethanol add >45 mic 150 ml acetic Simultaneous <90 mic Hydrothermaltreatment in  0 gm 800 gm 13 40.14 mg per gm  49.1 mg per gm acidadd >45 mic presence of 150 gm H₃PO₄ 4B: Parametric Variation: AceticAcid as Additive 200 ml acetic Sequential add <840 mic  No hydrothermaltreatment 50 gm 600 gm 14 31.89 mg per gm 41.16 mg per gm acid >45 mic15 34.59 mg per gm 36.70 mg per gm 300 ml acetic Sequential add <90 micHydrothermal treatment with  0 gm 600 gm 16 40.38 mg per gm 46.48 mg pergm acid >45 mic 150 gm H₃PO₄ 200 ml acetic Sequential add <90 micHydrothermal treatment with  0 gm 600 gm 17 40.87 mg per gm 49.3 mg pergm acid >45 mic 150 gm H₃PO₄ 150 ml acetic Sequential add <90 micHydrothermal treatment with 50 gm 600 gm 18 37.29 mg per gm 37.78 mg pergm acid >45 mic 150 gm H₃PO₄ 370 ml acetic Sequential add <90 micHydrothermal treatment with 50 gm 600 gm 19 43.07 mg per gm — acid >45mic 50 gm H₃PO₄ 4C: Parametric Variation: Amount of Phosphoric Acid 375ml Sequential add <90 mic High temp precip and 50 gm 600 gm 20 37.1 mgper gm — isopropanol >45 mic continuous heating 21 38.2 mg per gm — 375ml Sequential add <90 mic High temp precip and 50 gm 570 gm 22 34.16 mgper gm — isopropanol >45 mic continuous heating 375 ml Sequential add<90 mic High temp precip and 50 gm 550 gm 23   44 mg per gm —isopropanol >45 mic continuous heating 375 ml Sequential add <90 micHigh temp precip and 50 gm 500 gm 24 38.98 mg per gm — isopropanol >45mic continuous heating 375 ml Sequential add <90 mic High temp precipand 50 gm 300 gm 25 33.78 mg per gm — isopropanol >45 mic continuousheating 375 ml Sequential add <840 mic  Hydrothermal treatment with 50gm 450 gm 26 32.04 mg per gm 41.14 mg per gm isopropanol >90 mic 150 gmH₃PO₄ 150 ml 95% Simultaneous <90 mic No hydrothermal treatment 50 gm500 gm 12  32.9 mg per gm  42.2 mg per gm methanol add >45 mic 150 mlacetic Simultaneous <90 mic Hydrothermal treatment in  0 gm 800 gm 1340.13 mg per gm 49.11 mg per gm acid add >45 mic presence of 150 gmH₃PO₄ 41.06 mg per gm 46.84 mg per gm 250 ml acetic Simultaneous <90 micHydrothermal treatment in  0 gm 1000 gm  27 39.24 mg per gm 42.29 mg pergm acid add >45 mic presence of 150 gm H₃PO₄ (2.6 L water) 250 ml aceticSimultaneous <90 mic Hydrothermal treatment in  0 gm 1200 gm  28 39.24mg per gm  41.1 mg per gm acid add >45 mic presence of 150 gm H₃PO₄ (1.8L water) 250 ml acetic Simultaneous <90 mic Hydrothermal treatment in  0gm 1400 gm  29 40.80 mg per gm 49.18 mg per gm acid add >45 mic presenceof 150 gm H₃PO₄ (1 L water) 4D: Parametric Variation: Titrated ZP vs.Untitrated ZP 300 ml Sequential add <90 mic Hydrothermal treatment with65 gm 600 gm 30 30.1 mg per gm — isopropanol >45 mic no H₃PO₄ untitrated250 ml Sequential add <90 mic Hydrothermal treatment with 50 gm 600 gm31 30.63 mg per gm — isopropanol >45 mic no H₃PO₄ untitrated 200 mlSequential add <90 mic Hydrothermal treatment with 50 gm 600 gm 32 32.86mg per gm — isopropanol >45 mic no H₃PO₄ untitrated 300 ml Sequentialadd <90 mic High temp precip and 70 gm 600 gm 33,  28.6 mg per gm —isopropanol >45 mic continuous heating 34 untitrated 4E: ParametricVariation: Amount of Phosphoric Acid Used for Hydrothermal Treatment 300ml Sequential add <90 mic Hydrothermal treatment with 65 gm 600 gm 35  32 mg per gm — isopropanol >45 mic no additional H₃PO₄ 350 mlSequential add <90 mic Hydrothermal treatment with 50 gm 600 gm 36   35mg per gm — isopropanol >45 mic 50 gm H₃PO₄ 350 ml Sequential add <90mic Hydrothermal treatment with 50 gm 600 gm 37   44 mg per gm —isopropanol >45 mic 100 gm H₃PO₄ 350 ml Sequential add <90 micHydrothermal treatment with 50 gm 600 gm 38 48.37 mg per gm —isopropanol >45 mic 150 gm H₃PO₄ 4F: Parametric Variation: Room TempPrecip. With & Without Post-Hydrothermal Treatment vs. High Temp Precip.& Continuous Heating 375 ml Sequential add <840 mic  Room temp precipand no 50 gm 600 gm 39 36.07 mg per gm 40.20 mg per gm isopropanol >45mic hydrothermal treatment 40 30.55 mg per gm 40.48 mg per gm 41 35.01mg per gm 40.23 mg per gm 375 ml Sequential add <90 mic Hydrothermaltreatment with 50 gm 600 gm 42 44.75 mg per gm 58.61 mg per gmisopropanol >45 mic 150 gm phosphoric acid 43 43.46 mg per gm 47.22 mgper gm 44 42.05 mg per gm 47.56 mg per gm 375 ml Sequential add <840mic  Hydrothermal treatment with 50 gm 600 gm 45 36.05 mg per gm 43.43mg per gm isopropanol >45 mic 150 gm phosphoric acid 46 38.28 mg per gm45.36 mg per gm 47 37.07 mg per gm 45.81 mg per gm 375 ml Sequential add<90 mic High temp precip and 50 gm 600 gm   32A 32.86 mg per gm N/Aisopropanol >45 mic continuous heating   31A 30.63 mg per gm 48 37.02 mgper gm   30A 30.10 mg per gm   35A 32.00 mg per gm 49 30.15 mg per gm 5030.40 mg per gm 51 29.75 mg per gm 21 38.20 mg per gm 20 37.10 mg per gm4G: Parametric Variation: Amount of Isopropanol 350 ml Sequential add<90 mic Hydrothermal treatment with 50 gm 600 gm 52 36.88 mg per gm48.44 mg per gm isopropanol >45 mic 150 gm H₃PO₄ 300 ml Sequential add<90 mic Hydrothermal treatment with 50 gm 600 gm 48 37.02 mg per gm —isopropanol >45 mic no add H₃PO₄ 250 ml Sequential add <90 micHydrothermal treatment with 50 gm 600 gm   31B 37.52 mg per gm —isopropanol >45 mic no add H₃PO₄ 200 ml Sequential add <90 micHydrothermal treatment with 50 gm 600 gm 53 34.13 mg per gm 41.85 mg pergm isopropanol >45 mic 150 gm H₃PO₄ 4H: Parametric Variation: Using SodaAsh as Additive 40 gm soda Simultaneous <180 mic  Hydrothermal treatmentin  0 gm 600 gm 54 36.49 mg per gm 43.25 mg per gm ash addition >45 micpresence of 150 gm H₃PO₄ 40 gm soda Simultaneous <180 mic  Nohydrothermal treatment  0 gm 600 gm 55 35.35 mg per gm 37.95 mg per gmash addition >45 mic 40 gm soda Simultaneous <180 mic  No hydrothermaltreatment  0 gm 600 gm 56 39.91 mg per gm 41.74 mg per gm ashaddition >45 mic 30 gm soda Simultaneous <180 mic  Hydrothermaltreatment in  0 gm 600 gm 57 38.42 mg per gm 42.33 mg per gm ashaddition >45 mic presence of 150 gm H₃PO₄ 4I: Parametric Variation:Particle Size 375 ml Sequential add <840 mic  Hydrothermal treatmentwith 50 gm 600 gm 45 36.06 mg per gm 43.43 mg per gm isopropanol >45 mic150 gm H₃PO₄ 58 37.75 mg per gm 47.74 mg per gm 59 36.67 mg per gm 43.14mg per gm 46 38.28 mg per gm 45.36 mg per gm 47 37.07 mg per gm 45.81 mgper gm 375 ml Sequential add <90 mic Hydrothermal treatment with 50 gm600 gm 43 43.46 mg per gm 47.22 mg per gm isopropanol >45 mic 150 gmH₃PO₄ 44 42.05 mg per gm 47.56 mg per gm 42 44.75 mg per gm 58.61 mg pergm 60 37.95 mg per gm 45.21 mg per gm 61 38.30 mg per gm 41.14 mg per gm62 38.34 mg per gm 48.27 mg per gm 63 48.90 mg per gm 56.58 mg per gm  38A 48.37 mg per gm 58.38 mg per gm 64 41.71 mg per gm 45.10 mg per gm65 43.47 mg per gm 47.88 mg per gm 375 ml Sequential add <45 micHydrothermal treatment with 50 gm 600 gm 66 40.99 mg per gm 48.28 mg pergm isopropanol 150 gm H₃PO₄ 4J: Repeat of Sample Adsorption Test inDialysate (105 mEq/L NaCl, 35 mEq/L NaHCO₃) Plant ZP Control 67 17.49719.612 mg per gm mg per gm 150 ml acetic Simultaneous <90 micHydrothermal treatment in  0 gm 800 gm 68 20.107 24.77 mg per gm acidadd >45 mic presence of 150 gm H₃PO₄ mg per gm 250 ml aceticSimultaneous <90 mic Hydrothermal treatment in  0 gm 1400 gm  69 20.04425.007 acid add >45 mic presence of 150 gm H₃PO₄ mg per gm mg per gm 40gm soda Simultaneous <180 mic  Hydrothermal treatment in  0 gm 800 gm 7020.991 28.193 ash add >45 mic presence of 150 gm H₃PO₄ mg per gm mg pergm

Product Quality-Cartridge Performance Test

The particles for some of the sol gel samples were evaluated for sorbentcartridge application based on NH₄ ⁺—N adsorption capacity of thecartridge, and the flow resistance pressure as well as the leakagebehavior of it, according to the procedure as follows.

The cartridge was assembled as shown in FIG. 1 by the followingconfiguration using 800 gm of sol gel ZP in the REDY cartridge canister.In testing the NH₄ ⁺—N capacity of the cartridge, it was first primedwith 12 L dialysate (105 mEq/L NaCl; 35 mEq/L NaHCO₃). Afterwards, 54 Ldialysate containing 50 mg/dL NH₄ ⁺—N in the form of (NH₄)₂CO₃ wassingle passed through the cartridge to simulate the composition afterhydrolysis of urea. The single pass flow rate of the solution wasmaintained at 250 ml/min until NH₄ ⁺—N breaks through at the level above2 mg/dL. The residual volume of the unused (NH₄)₂ CO₃ solution wasrecorded and the NH₄ ⁺—N adsorption capacity of the cartridge wascalculated based on the following calculations:

NH₄ ⁺—N adsorption capacity of cartridge=0.5 gm NH₄ ⁺—N/L×0.25L/min×breakthrough time in min.  (i)

0.5 gm NH₄ ⁺—N/L×(54 L−residual volume in L).  (ii)

The flow dynamics of the cartridge was examined by spraying thecross-section of the ZP layer with the NH₄ ⁺ indicator solution toreveal the unused ZP used for NH₄ ⁺—N adsorption. The NH₄ ⁺—N capacityfor the 800 gm ZP cartridge was re-calculated by taking into account theunused portion.

The results for cartridge tests for various sol gel ZP samplesrepresenting embodiments of the present invention and comparison with aBZS ZP sol gel as a control are indicated in Table 5.

TABLE 5 Cartridge Test Results Summary in Comparison with BZS ZP NH₄ ⁺—NPredicted NH₄ ⁺—N Adsorption % UNC if Flow Cartridge Design BreakthroughCapacity Unused ZP fully resistance Test No. Features ZP Quality andPreparation Time at B.T. ZP utilized pressure 1 1 thin cellular Plant ZP195 min 25.2 gm 5% 26.5 gm   12.5 psi max (control) sponge; blended withglass beads 2 Regular Particle size: <90μ 135 min 16.4 gm 40% 27 gm   22psi max packing Adsorption: 47 mg NH₄ ⁺—N per gm Prep: isopropanoladditive; sequential addition and hydrothermal treatment (Sol Gel ZP #37, 60) 3 Regular Particle size: <90μ 128 min   17 gm 50% 34 gm  >30 psimax packing Adsorption: 47 mg NH₄ ⁺—N per gm Prep: isopropanol additive;sequential addition and hydrothermal treatment (Sol Gel ZP # 65, 64) 4Regular Particle size: <90μ  97 min 12.5 gm 55% 28 gm   31 psi maxpacking Adsorption: 48 mg NH₄ ⁺—N per gm Prep: isopropanol additive;sequential addition and hydrothermal treatment (Sol Gel ZP # 38A, 63) 5¾ inch air Particle size: <90μ 110 min   13 gm 70% 43 gm   9 psi maxspace above Adsorption: 45 mg NH₄ ⁺—N per gm ZP layer Prep: acidic acidadditive; sequential addition and hydrothermal treatment (Sol Gel ZP #17, 16) 7 ¼ inch air Particle size: <90μ 180 min 20.7 gm 20% 26 gm 21.5psi max space above Adsorption: 45 mg NH₄ ⁺—N per gm ZP layer Prep:isopropanol additive; sequential addition and hydrothermal treatment(Sol Gel ZP # 42, 44) 8 ¼ inch air Particle size: <250μ  45 min   6 gm90% —  6.5 psi max space above Adsorption: 47 mg NH₄ ⁺—N per gm ZP layerPrep: isopropanol additive; sequential addition and hydrothermaltreatment (Sol Gel ZP # 58, 45) 9 2 rings Particle size: <250μ 150 min18.8 gm 35% 29 gm   9 psi max Adsorption: 45 mg NH₄ ⁺—N per gm Prep:isopropanol additive; sequential addition and hydrothermal treatment(Sol Gel ZP # 59, 47, 45) 10  Thick cellulose Particle size: <250μ 150min 20.7 gm 20% 26 gm   16 psi max sponge; 2 Adsorption: 40 mg NH₄ ⁺—Nper gm rings Prep: isopropanol additive; sequential addition and NOhydrothermal treatment (Sol Gel ZP # 41, 40) 11  Thick celluloseParticle size: <90μ 135 min 16.7 gm 30% 24 gm 16.5 psi max sponge; 1ring Adsorption: 47 mg NH₄ ⁺—N per gm Prep: acetic acid additive;sequential addition and hydrothermal treatment (Sol Gel ZP # 17, 16) 12 Thick cellulose Particle size: <90μ 195 min   20 gm 20% 25 gm   13 psimax sponge; Adsorption: 42 mg NH₄ ⁺—N per gm blended with Prep:isopropanol additive; glass beads simultaneous addition and NOhydrothermal treatment (Sol Gel ZP # 1) 13  Thick cellulose Particlesize: <90μ 150 min 19.8 gm 20% 25 gm 15.5 psi max sponge; Adsorption: 45mg NH₄ ⁺—N per gm blended with Prep: acetic acid additive; glass beadssimultaneous addition and hydrothermal treatment (Sol Gel ZP # 4, 5) 14 1 thin cellulose Particle size: <90μ 135 min 19.4 gm 30% 28 gm   29 psimax sponge; Adsorption: 45 mg NH₄ ⁺—N per gm blended with Prep:isopropanol additive; glass beads simultaneous addition and NOhydrothermal treatment (Sol Gel ZP # 6) 15  2 thin cellulose Particlesize: <180μ 135 min   16 gm 25% 21 gm   11 psi max sponges Adsorption:49 mg NH₄ ⁺—N per gm Prep: Max amount of H_(3PO4) (Sol Gel ZP # 13, 29)16  2 thin cellulose Particle size: <180μ 140 min   18 gm 25% 24 gm  9.5psi max sponges Adsorption: 43 mg NH₄ ⁺—N per gm Prep: Soda ash additive(Sol Gel ZP # 54, 55)

The BET surface area, pore volume, monolayer volume, and pore sizedistribution of six sol gel ZP samples were analyzed by using differentadditives and processing conditions, in comparison with the BZS ZPproduct as a control. BET surface area can be measured by knownstandards, such as ASTM D 6556. Nitrogen is the typically usedadsorptive for surface area determinations. All BET values indicatedherein are inclusive of at least BET nitrogen surface area. Other gasesmay be used, such as krypton or argon. The pore volume, (Langmuir)monolayer volume, and pore size distribution can be determined by anadsorption method or mercury porosimetry. All pore volume, monolayervolume, and pore size distribution values indicated herein are inclusiveof values determined using mercury porosimetry. As indicated, the porevolumes and pore sizes also can be determined with adsorption methodsknown in the industry. The BET surface area, pore volume, monolayervolume, and pore size distribution can be measured, for example, using acommercial porosimetry designed to make these various analyses, such asMicromeritics Autopore series porosimeters, or by other porosimetryinstruments and/or techniques that are applicable to ZrP.

The results for BET surface area, pore volume, monolayer volume, andpore size determinations for various sol gel ZP samples representingembodiments of the present invention and comparison and control sol gelsare indicated in Table 6.

TABLE 6 BET Surface Particle Size Area Pore volume Monolayer volume Poresize Sample No. Preparation Method (microns) m²/gm Ml/gm Ml/gm (STP) Nm 8 Using alcohol additive <90 (incl. 14.17 0.0363 3.2557 20-80 (45.92%)without hydrothermal fines) treatment  7 Using acetic acid additive45-90 27.136 0.0802 6.2347 20-80 (48.85%) without hydrothermal treatment(with HCl) 56 Using soda ash additive  45-180 2.458 0.007 0.5649 20-80(35.79%) without hydrothermal treatment 13 Using acetic acid additive45-90 2.245 0.008 0.5158 20-80 (40.57%) without hydrothermal treatment(without HCl) 54 Using soda ash additive  45-180 1.499 0.0063 0.344520-80 (34.91%) with hydrothermal treatment 29 Using high phosphoric acid45-90 2.425 0.0076 0.5571 20-80 (33.62%) and acetic acid additive ZPCtrl-BZS 1.622 0.0065 0.3726 20-80 (39.89%) ZP Control Sample

The effect of swelling of sol gel ZP on cartridge design wasinvestigated by measuring the difference in particle density of thematerial in dialysate and cyclohexane for various sol gel ZP samplesrepresenting embodiments of the present invention and comparison orcontrol sol gel ZP samples.

The results for the swelling tests are indicated in Table 7 and shown inFIG. 2.

TABLE 7 Swelling Volume Sample # Additive (cm³/50 g) (cm³/kg)Hydrothermal treatment 9 Methanol 1 20 57 Soda ash 4 80 18 Acetic acid 240 26 Isopropanol 2 40 No Hydrothermal Treatment 67 Control 1 20 8Methanol 3 60 56 Soda ash 2 40 14 Acetic Acid 1.5 30 21 Isopropanol 0.12

Results and Discussions:

With respect to result for NH₄ ⁻N adsorption quality of product, the solgel ZP has about 100% improvement over the BZS ZP product, which has NH₄⁺—N adsorption capacity of about 20 mg/g ZP. As shown in Table 4, theNH₄ ⁺—N adsorption capacity of sol gel ZP may vary with the processconditions. These conditions are further discussed below in order to,for example, guide maximization of NH₄ ⁺—N adsorption quality ofproduct, prevent excessive agglomeration upon drying, and formation offine particles.

With respect to mixing weight ratio of ZOC to H₃PO₄, the resultsindicate that the increase of the mixing weight ratio of ZOC to 76%H₃PO₄ from 500 g:600 g to 500 g:800 g can increase the NH₄ ⁺—Nadsorption capacity from about 45 mg/gm ZP to 49 mg/gm ZP. However, nomore improvement appears to be attainable upon increasing the amount of76% H₃PO₄ further, even up to 500 g:1400 g, although the product is morecrystalline when the amount and concentration of H₃PO₄ increase.Furthermore, cartridge performance test results indicate no differencein the NH₄ ⁺—N adsorption capacity by the cartridge as caused by suchimprovement of the material because, apparently, it is affected more bythe flow dynamics due to bed porosity and particle size of the material.Thus, the weight mixing ratio of ZOC to 76% H₃PO₄ at 500 g:600 g can beconsidered to be optimum for the sol gel process in view of this stageof experiments.

With respect to simultaneous addition of ZOC and H₃PO₄, simultaneousaddition of ZOC and H₃PO₄ helps to produce sol gel ZP particles withmore uniform composition and particle size during the precipitationreaction, thus reducing agglomeration of the product upon drying andformation of fine particles. Simultaneously, the NH₄ ⁺—N adsorptioncapacity of the product can be improved consistently to the range of 40mg/g ZP-45 mg/g ZP even without the need of hydrothermal treatment.

With respect to hydrothermal treatment, hydrothermal treatment of thecrude sol gel ZP in the presence of dilute H₃PO₄ is found to improve theNH₄ ⁺—N capacity of the product consistently to the range 40 mg/g ZP-45mg/g ZP. It has the advantage of improving the crystal structure andpoor adsorption quality of product caused by improper precipitationprocess (e.g. sequential addition instead of simultaneous addition ofZOC and H₃PO₄). The method is simply heating the crude sol gel ZP slurryin DI or RO water to about 90° C. and maintaining the temperature forabout 1 hour, with the concentration at about 500 gm per 2 L and 150 gm76% H₃PO₄ added to the slurry before the heating.

With respect to the type of additive to ZOC and its amount, thefollowing types and amounts of additives to the ZOC solution shown inthe Table below are found to be effective to prevent gelation of theproduct during the precipitation process and improve the NH₄ ⁺—Nadsorption of it by enhancing its porosity.

TABLE 8 Amount based on NH₄ ⁺—N adsorption Type of additive 500 gm ZOCcapacity of product Alcohol (isopropanol or 300 ml 40-45 mg NH₄ ⁺—N/gm95% methanol) ZP Acetic acid 200 ml 40-45 mg NH₄ ⁺—N/gm ZP Soda ash  40gm 40-42 mg NH₄ ⁺—N/gm ZP

As indicated, the BET surface area, pore volume and pore sizedistribution of six sol gel ZP samples were analyzed by using differentadditives and processing conditions, in comparison with the BZS ZPproduct as control are shown in Table 6. Although there is no directrelationship between the gas adsorption and the ion-exchange reactionwith NH₄ ⁺—N, the data in general indicates that sol gel ZP is moreporous than the BZS ZP.

With respect to the amount of concentrated HCl added to ZOC, theparticle size of sol gel ZP can optionally be improved by adding a smallamount of concentrated HCl to the ZOC solution (about 40 ml per 650 mlZOC solution). The particle size of precipitate can then be controlledto a desirable range in combination with the agitation rate and optionalconcentration of H₃PO₄.

With respect preliminary cartridge performance, as shown in Table 5,preliminary cartridge performance of using sol gel ZP prepared accordingto various conditions can be summarized as follows. With regard to theeffect of swelling of sol gel ZP on cartridge design, the high porosityof sol gel ZP can cause an initial swelling of the ZP bed in thecartridge by the absorption of the dialysate saturated with CO₂ gas,followed by the shrinkage of the bed as the CO₂ gas level in dialysateis reduced. The swelling data of some typical sol gel ZP samplesprepared by different additives and processing conditions in comparisonwith that of BZS ZP are shown in Table 7 and FIG. 2. As indicated, thedata is taken by measuring the difference in particle density of thematerial in dialysate and cyclohexane. It can be seen that sol gel ZP ingeneral has more swelling than BZS ZP.

With respect to the effect of particle size on NH₄ ⁺—N leakage and flowresistance pressure, sol gel ZP with particle size sieved between 45microns and 90 microns does not cause any flow resistance (with backpressure less than 12 psi) when a sponge is put above the ZP layer.Furthermore, sol gel ZP sieved below 180 microns has no NH₄ ⁺—N leakageeven though the bed is loosely packed. This indicates the sol gel ZP canadsorb NH₄ ⁺—N rapidly due to the high porosity or sponge nature of thematerial.

With respect to correlation of cartridge urea-N capacity to NH₄ ⁺—Ncapacity data of material, a consistent 17 gm-20 gm UNC is obtainablewith no NH₄ ⁺—N leakage when 800 gm sol gel ZP is used in the REDYcartridge despite less than optimal flow causing about 30% unused ZP forNH₄ ⁺—N adsorption. The UNC is expected to be increased when thematerial is used in a bigger canister causing a slower flow velocity andhence a more uniform flow.

With respect to process performance, when a sufficient amount ofalcohol, acetic acid or soda ash is added to the ZOC solution, there isno gelation problem in the sol gel ZP precipitation process. The productmaterial can be filtered easily during the washing process and noagglomeration occurs upon drying.

With respect to process efficiency, sol gel ZP precipitation process atambient temperature can be easily performed and can greatly increase theefficiency of making ZP especially when no hydrothermal treatment isinvolved. The simultaneous addition of ZOC and H₃PO₄ can improve theadsorption quality of the product to the extent such that thehydrothermal treatment can be skipped.

With respect to particle size control and amount of fine particles,particle size control of the product can be facilitated by making thesol gel ZP particle size a little bigger during the precipitationprocess (90-180) microns followed by grinding the dried product powderto the desirable range with a particle size control grinder. The amountof fine particles (below 45 microns) in a lab scale batch can be lessthan 5%.

The sol gel process of the present invention is the highly efficient andeconomical method of manufacturing ZP when the gelation problem has beensolved by using additives to the ZOC solution according to the presentinvention. These results indicate an enhanced design of the sol gelprocess can be expected to produce ZP product with NH₄ ⁺—N adsorptioncapacity of (40-45) mg/g, which is about 80% higher than that of thecurrent product.

In these studies, a cartridge using 800 gm sol gel ZP removes only 17 to20 gm NH₄ ⁺—N from dialysate with about 30-35% unused ZP, which isthought to predict that a urea-N capacity of 30 gm can be attainablewhen the material is fully utilized in NH₄ ⁺—N adsorption, such as forsorbent dialysis.

Applicant specifically incorporates the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1-28. (canceled)
 29. Zirconium phosphate (ZrP) particles having thefollowing characteristics: an average particle size of about 45-90microns, a BET surface area of at least 2 m²/g ZrP, and an ammoniacapacity in dialysate of at least about 15 mg NH₄—N/g ZrP, at 20 mg/dLNH₄—N.
 30. The particles of claim 29 having a BET surface area of atleast 10 m²/g ZrP.
 31. The particles of claim 29 further having a porevolume of at least 0.0071 mL/g, a monolayer volume of at least 0.5 mL/g(STP), and a 20-80 nm pore size content of at least 30%.
 32. A dialysiscartridge comprising a cartridge that contains the zirconium phosphateparticles of claim
 29. 33. Zirconium phosphate (ZrP) particles havingthe following characteristics: a pore volume of at least 0.0071 mL/g, amonolayer volume of at least 0.5 mL/g (STP), and a 20-80 nm pore sizecontent of at least 30%.
 34. A dialysis cartridge comprising a cartridgethat contains the zirconium phosphate particles of claim 33.